The present invention relates to the dental attachment that fixes denture in the mouth using magnetic attraction.
The prior dental magnetic attachment using magnetic attraction is shown in, for example, laid-open Japanese patent number 8-317941. This dental magnetic attachment comprises a magnetic assembly, which exerts the magnetic attractive force of a permanent magnet, and a keeper made of soft magnetic material that is attracted by the magnetic assembly. This magnetic assembly has a planar attractive surface that attracts the keeper, while the keeper has a surface that is attracted to the attractive surface of the magnetic assembly.
Though the attractive force of the dental attachment is strong in the direction of attraction, it is weak in the direction parallel to the attractive face.
Therefore, upon an external force in the oral cavity, the magnetic apparatus usually shifts in the direction parallel to the attractive face. That is, the magnetic apparatus moves parallel to the keeper and slips out of place, forming a considerable gap.
This gap lowers the magnetic attractive force causing the denture to come off easily. And this gap, which never occurs with natural teeth, also gives an unnatural feeling when chewing, and makes chewing with the denture less comfortable.
As shown in FIG. 7, laid-open Japanese patent number 11-276505 discloses a dental attachment that has a concave part 50 in a portion of the circumference of yoke 5 made of soft magnetic material in the magnetic assembly 8, and a convex part 60 in a portion of the circumference of keeper 6 made of soft magnetic material.
This invention aims to prevent the slipping out of place of the magnetic apparatus as seen in prior dental attachments by using said convex and concave parts.
FIG. 8 shows the arrangement of this dental attachment in a denture. The keeper 6 is cast in the root cap R, and the root cap R is embedded in the tooth root S. The magnetic assembly 8 is embedded in the denture T.
However, in this invention shown in FIG. 7, if while fitting the denture, one of the concave parts 50 in a portion of the circumference of the yoke 5 which is attracted to one of the concave parts 60 in a portion of the circumference of the keeper 6 embedded in the tooth root S, the magnetic assembly will be fixed in an inclined state. This makes it difficult to fix the attachment parallel to the attractive surface. Therefore application of the denture is difficult. Furthermore, removal is also difficult because the two components are fixed mechanically.
Accordingly, the present invention aims to offer a dental magnetic attachment, which is easy to fix and prevents movement and the formation of a gap between the magnetic assembly and the keeper.
The present invention is the dental attachment, which has a magnetic apparatus that exerts magnetic attraction and a keeper that is attracted to said magnetic apparatus. Said keeper has a convex part with a surface that is attracted by said magnetic apparatus. Said magnetic apparatus has a magnetic assembly, which has a built-in permanent magnet and an attractive surface, and a non-magnetic guide ring made of non-magnetic material that is arranged on the lateral face around said magnetic assembly. Said non-magnetic guide ring and said attractive surface of said magnetic assembly form a concave part which fits to said convex part of said keeper.
The present invention, the dental attachment, would allow relative movement between a magnetic apparatus and the keeper only within the admitted range between the concave part of the magnetic apparatus and the convex part of the keeper.
Therefore, the present invention allows for very little slipping and very little gap in the direction of attraction and in the direction parallel to the attractive face. Furthermore, this invention has a non-magnetic guide ring of the magnetic apparatus, made of non-magnetic material, which does not form a magnetic circuit in the combined convex and concave parts, so no magnetic attractive force acts in the combined parts.
In addition, while fitting a denture, even if one part of the magnetic apparatus comes near the keeper first, no strong magnetic force acts, which solves the problem of the magnetic assembly being fixed to the attractive surface in an inclined state and not being able to fix the attractive surface parallel because one part is fixed first. Therefore, it is easy to fix and remove the denture.
Furthermore, at least one part of the lateral face of said convex part of said keeper and at least one part of the inner lateral face of said non-magnetic guide ring could have a tapered part that could fit with each other.
This makes it easier to fix and remove the denture.
Also, at least one part of the inner lateral face of said non-magnetic guide ring and at least one part of the lateral face of said convex part of said keeper could have a straight part, providing an amount of friction between the adjacent straight faces. In this case, holding force similar to force between a body and a cap in a tea-caddy can be obtained.
And, said magnetic assembly comprises a yoke that is formed of a magnet inserting part with a bottom and lateral part, the permanent magnetic that is inserted in the magnet inserting part of the yoke, soft-magnetic shield plate comprising at least a part of said attractive surface over said permanent magnet, non-magnetic seal ring made of non-magnetic material between said soft magnetic shield and said yoke. Said non-magnetic guide ring is welded together with said yoke. The distance between said permanent magnet and the welded part, where said yoke is welded with said non-magnetic guide ring, is preferable to be the same or more than the thickness of said bottom of said yoke.
In this case, a decrease in magnetic force due to said weld can be avoided and excellent attraction can be achieved.